Spark Plug Gap question

[fowlerprowler]

Hello, I have hopefully a simple question dealing with spark plug gap. I have a 1997 Johnson 200 hp Venom and am putting new plugs in it. Went to the NGK guide and found the correct plugs (BPZ8HS-10). Everywhere I look the correct gap is .030 which has always seemed to be the gap for any outboard I've owned. BUT the local boat mechanic has said that the recommended gap for most plugs now is .040. I didn't question him, I just figured I'd look it up. Anyway, I pulled the old plugs out of my motor and they were gapped at .040. Now I bought this boat 2 years ago from a guy in a different state, 200 miles away. He had the boat serviced before I bought it so it had new plugs and such. His local mechanic gapped them that way. So whats the correct gap? Is there a reason for increasing the gap? Do I need to use the listed .030? Split the difference at .035? or go to the .040? and why? Thanks in advance.

 

[gm280]

Re: Spark Plug Gap question

WOW, looks like you may have opened up another can-of-worms issue here. There are many different point of view with spark plug gaps, as like which is the best 2-cycle oil questions... :laugh: The standard gap of .030" is basically the same for most all 2-cycle engines. If you open up that gap, you now are making your ignition coils work a little harder to actually jump that extra gap. It will give you a larger spark to help ignite the fuel/air mixture but works the system harder at the same time. And could even cause a lot more miss-firers too. The actual reasoning behind it is anybody's guess, maybe to keep fouling at a minimum. Unless the mechanic can give a convincing reason for opening the gap up, I'd follow the original manufacture's gap setting... The original manufacturer engineering their ignition system to withstand certain issues and that is what they determined to be the best compromise... But JMHO!

 

[Joe Reeves]

Re: Spark Plug Gap question

The original recommended plug gap back when the "Magneto Capacitance Discharge" ignition system came into existence (your ignition system) was .040 and this held true up until the late 1990's when the recommended gap was changed to .030.

The reason for the change was really just to prolong the spark plug life as the .040 gap would wear the electrodes pretty bad usually in one season if one was more than an occasional weekend boater.

However, it has been found that one gap or the other would provide a somewhat improved performance at idle or the higher rpm setting on various models... one year and hp may do better at idle, another of the same year and model may do better at full throttle, using the same plug gap... and nobody seems to know why. So.................

If the .030 gap works fine at idle and full throttle, that's the way to go as the spark plug will last longer. If a performance problem pops up at one rpm range or the other, try the .040 gap to see if it makes a difference before going the repair route

 

[Tim Frank]

Re: Spark Plug Gap question

Went to the NGK guide and found the correct plugs (BPZ8HS-10). Everywhere I look the correct gap is .030 which has always seemed to be the gap for any outboard I've owned. BUT the local boat mechanic has said that the recommended gap for most plugs now is .040. .....

The OEM recommended plug is Champion QL78YC gapped at 0.030".

The Champion/NGK debate often gets contentious in here.
All I'll say is that I personally have not had good results with running NGK plugs in OMC products....which is absolutely not a criticism of NGK...just noting that when a plug manufacturer states that their plug is "equivalent" to another manufacturers plug, don't count on it.

 

[fowlerprowler]

Re: Spark Plug Gap question

Appreciate it guys. Don't even want to start a "discussion" on NGK versus Champion. I thought of the wider gap to get a hotter spark but didn't think of the small amout of extra work required by the ignition coils so thanks for that thought. I'm going to go with the .030" as recommended by everything I read and since I'm so used to using that gap on other outboards. Again, appreciate the information.

 

[Tim Frank]

Re: Spark Plug Gap question

I'd recheck the source for your selection of the NGK plug....that may be too cold a plug.

Heat Range Conversion Chart

That being said, the final result is all that matters....if your engine is running well and the plugs show the optimal colour and wear you are home and dry. There is definitely a bit of witchcraft involved in getting a "perfect " match.

 

[fowlerprowler]

Re: Spark Plug Gap question

One source was this website, iboats. 200 hp Venom LV6 1994-2003 calls for the BPZ8HS-10. Don't remember the site but I crossed referenced that NGK with other possible plugs and the Champion QL78YC as you mentioned came across as an equivalent plug. I checked all this on the front end since this was the first set of plugs I was putting in it. The plugs I pulled out of it were Champion QL82YC. I have no idea why those were in it but I kept the number (and the old plugs) in case of issues switching to a different plug. I'll have it on the water tomorrow and see how it does. Only problem with the motor has been that it is hard to get started first thing. Once it's been started, it will fire up fine the rest of the day. The guy I bought it from told me that and he wasn't lying . The old plugs were very clean and looked to be in good shape for 2 year old plugs. I was changing them because they were 2 year old plugs and they didn't match what it was calling for the motor.

 

[fowlerprowler]

Re: Spark Plug Gap question

One other reason for changing the plugs at 2 years was back in my bass tourny days, my other boats I've had, I'd change the plugs out once a year. Main reason was I would run those motors 3 to 5 times a week, 10 months out of the year. And it was nothing to take off from the ramp and run wide open for 10 to 15 miles. And then a lot of short wide open runs. My previous motors were a 1986 Johnson 175 hp on a 19' skeeter and a 1991 Johnson 175 hp on a 19' Javelin. Plugs wouldn't last 2 years running like that or atleast would not be in real good shape at 2 years. The boat I have the 200 hp Johnson on now is a 21' Triton Fish & Ski that only gets used 15 to 20 times a year. And I hardly ever open it up. I'm either running at cruizing speed with the motor turning 4500-5000 RPM's or the motor is tucked under the boat turning 3000 RPM's pulling a tube with my kids on it. So I would think plugs should easily last two years or better running like that. But again, I've only had this boat two years and have yet to get a feel how long the plugs should last.